Challenges present and future in the observation of the Cosmic Microwave Background

Transcription

1 Challenges present and future in the observation of the Cosmic Microwave Background Aniello (Daniele) Mennella Università degli Studi di Milano Dipartimento di Fisica

2 Today

3 Today We're looking at the universe when it came to light almost 14 billions years ago. And we're looking at the best picture we could possibly get. This is beautiful and we should not forget that this possibility is far from being obvious

4 We know how much stuff there is in the universe

5 We see dark matter through CMB lensing

6 Remarkable agreement

7 Remarkable agreement This is indeed precision cosmology But: is the situation completely analogous to FIRAS measurement?

8 ΛCDM: a mathematical miracle? (Tomasi, 2013) One acronym, two mysteries Cold dark matter Dark energy

9 The tip of the iceberg The physics of gravity in the early universe is still to be unveiled

10 Wandering in bright fog Today's BIG questions What is the nature of dark matter? Does dark energy exist, what is its nature? Is it constant or does it modify with time? Or is it necessary to invoke a modification of General Relativity at large scales? Or of its assumptions? Did inflation occur? In which conditions? When did the first stars form and in which conditions? These are big and deep questions, indeed. The CMB is still key to address many of them

11 The shadow of the giants Cosmology with the SZ effect Planck 2013, XX.

12 The shadow of the giants Cosmology with the SZ effect From quasar absorption lines Luzzi et al, ApJ, 2009 We'll soon see points from Planck to this plot From SZ measurements

13 Cosmic glasses Cosmic matter distribution through CMB lensing Planck 2013, XVII astro-ph > arxiv:

14 Total blackness The quest for distortions of the CMB spectrum No distortions found over more than 3 decades in frequency

15 Total blackness The quest for distortions of the CMB spectrum ApJ, 2011, 734 Last results from ARCADE 2, report low frequency excess NOT of cosmological origin

16 before the next one The ultimate veil: CMB polarisation

17 Tensor B-modes: a quest for the Sacred Graal Nobody has seen them. Nobody knows where they are, if they are.

18 Tensor B-modes: a quest for the Sacred Graal To detect tensor B-modes we want, at minimum, to detect the maximum with high statistical significance

19 Tensor B-modes: a quest for the Sacred Graal High angular resolution is not an issue, purity of measurements over large angular scales is

20 Latest results QUIET collaboration, ApJ 2012

21 Latest results QUIET collaboration, ApJ 2012

22 BIG challenges Sensitivity to hit the B-mode maximum at the lowest possible value of r (Relatively) large sky coverage Control of systematic effects at the sensitivity level Accurate calibration Control of polarized foregrounds

23 Challenge # 1 Meeting the sensitivity Experiment duration (days) Photon noise limited detectors (Tnoise = 0) 60 fsky = 30 % S/N = 1 40 Bandwidth = 20 GHz 20 for Duty cycle =

24 Challenge # 1 Meeting the sensitivity Constant ~ 1, dependent on receiver architecture Experiment duration (days) Photon noise limited detectors (Tnoise = 0) 60 fsky = 30 % S/N = 1 40 Bandwidth = 20 GHz 20 for Duty cycle =

25 Challenge # 1 Meeting the sensitivity Number of receiver units detecting Q and U Experiment duration (days) Photon noise limited detectors (Tnoise = 0) 60 fsky = 30 % S/N = 1 40 Bandwidth = 20 GHz 20 for Duty cycle =

26 Challenge # 1 Meeting the sensitivity Experiment duration (days) Wband HEMT detectors (Tsky + Tnoise = 40K) 60 fsky = 30 % S/N = 1 40 Bandwidth = 20 GHz 20 for Duty cycle = Bolometers

27 TES detectors (ground) Bolometric interferometer 2016 TES bolometric detectors (in some cases coupled to planar antennas) provide state-of-the-art sensitivity and maximum compactess 2014 PolarBear TES bolometers

28 Battistelli et al, Astrop. Phys, 2011 New tecnique applied to bolometric CMB measurements Planned for observations from DOME-C Potential advantages in systematic effects control and calibration

29 TES detectors (balloon) LSPE Use of multimodal feed-horns! (SWIPE) SPIDER EBEX

30 HEMT detectors QUIET design Developed at JPL (Todd Gaier et al) Compact, on-chip receiver design Pseudo correlation polarimetry (detects Q/U simultaneously) Applied in QUIET and LSPE Benign to systematic effects ~ 5 43 GHz, ~ GHz Significant noise improvements with last generation InP devices (35 nm gate technology, not implemented yet)

31 HEMT detectors QUIET LSPE (STRIP)

32

33 Azimuth Pivot SWIPE Bolometers ( GHz) Spin 3 rpm STRIP HEMT (43 90 GHz) Al frame Star Sensor Batteries + Electronics The height of the gondola for this configuration is about 4.5 m

34 Azimuth Pivot SWIPE Bolometers ( GHz) Spin 3 rpm STRIP HEMT (43 90 GHz) Star Sensor Al frame Polarimeters with QUIET design Batteries + Electronics The height of the gondola for this configuration is about 4.5 m

35 SWIPE Bolometers ( GHz) Azimuth Pivot foam window Spin HWP 3 rpm HDP Lens STRIP HEMT (43 90 GHz) Array 2 He Fridge 3 Al frame Star Sensor Array 1 4 He Batteries + Electronics The height of the gondola for this configuration is about 4.5 m

36 Challenge # 1 Meeting the sensitivity Larger arrays being designed and developed TES and InP technology improvements allow manufacturing of large focal planes Use of multi-modal horns can be explored to further increase array sensitivity Challenge is tough, but roads lay ahead

37 Challenge # 2 Meeting the sky coverage Experiments from ground Balloon experiments

38 LDB flights in the Arctic night Svalbard islands provide a very good opportunity to launch long duration balloons during the Arctic night. OLIMPO (launch in summer 2014) will be the first ballon to perform a complete circle around the North Pole Test flight #1 Summer 2007 Test flight #2 Winter 2011

39 LSPE Sky coverage Tomasi Post-doc \ Krachmalnicoff PhD student

40 Challenge # 2 Meeting the sky coverage Telescope arrays from ground and long duration flights during polar nights are most promising short term solutions Main challenges are Telescope arrays: coordinate and harmonize measurements from different telescope / sites LDB flights in polar night: stratospheric currents around North Pole less known than around South Pole Space is the ultimate challenge for total sky coverage

41 Challenge # 3 Meeting the systematic effects control

42 Planck 2013, III LFI systematic uncertainties

43 Systematic effects have been carefully studied and controlled during Planck development They challenge us at the largest angular scales, especially in polarization Deep instrument knowledge and in-hardware control of effects is mandatory for ultra-high sensitivity future experiments

44 Optical Beam ellipticity / cross polarization Sidelobes (Earth, Sky pickup) Polarization I Q/U leakage Q U leakage Noise and stability 1/f noise Thermal stability Cosmic ray hits Time constants Pointing Pointing uncertainties Electronics ADC non linearities DC spurious signals

45 Main beams Symmetrical beams are required to minimize cross polarization Possible solutions: (1) on-axis lenses (like, e.g. SPIDER, LSPE-SWIPE), (2) off-axis reflectors (like Crossed-Dragone configurations used by QUIET, ABS, LSPE-STRIP) Simulation of impact of beam asymmetries recommended

46 STRIP crossed Dragone dbi Villa, 2012 INAF-Bologna Sandri, 2012 INAF-Bologna Cross-pol ranging from -37 to -50 db

47 Assessing impact of beam asymmetries

48 Sidelobes Pickup of polarized sky or earth signals by beam sidelobes can introduce a large systematic uncertainties Typical requirements for LSPE are ~ -70 db (tough!) Simple reflective baffles can be not enough (sidelobes are redirected towards the sky) evaluating possibility of a warm stop Corrugated feed horns are still the best choice for best optical performance

49 Platelet corrugated feeds Patelet feeds can be manufactured in series with much lower costs compared to other techniques (e.g. electroforming) already implemented, e.g., in QUIET 43 GHz LSPE-STRIP Del Torto Post-doc 95 GHz prototype study Franceschet PhD student 150 GHz QUBIC prototype Cavaliere Head of mechanical shop

50 I Q/U leakage One of the most critical effects Can arise because of various depending on the instrument (e.g. bandpass mismatches, OMT or polarizer non idealities) Needs be kept below 0.1% Krachmalnicoff, 2013

51 Noise and stability LSPE-STRIP (QUIET) 43 GHz noise simulations Large angular scale experiments require high level of stability Aggressive filtering impacts signal on large angular scales Knee frequencies of order of mhz or less are required Coherent polarimeters offer an advantage Krachmalnicoff, 2013

52 Challenge # 3 Meeting the systematic effect control Very tough challenge. Current level of systematic effects in polarization experiments can still be marginal for robust B-mode detections, especially at low-ell. Optics, polarization leakage, sidelobes control are critical. Simulations and in-hardware control (as much as possible) are key

53 Challenge # 4 Meeting the calibration accuracy

54 Challenge # 4 Meeting the calibration accuracy Planck 2013, V

55 Challenge # 4 Meeting the calibration accuracy Planck 2013, V Planck photometric calibration for temperature data is < 1 % and will have to be improved for next release

56 Accurate calibration in polarimetry Internal calibrators: useful, may be difficult in balloon experiments (Boomerang achieved 0.1% with internal calibration lamp) Few well known natural polarized calibrators (Crab nebula). No well know diffuse calibrators, unfortunately! Polarization angle: needs be know better than 1 Main beams: needs be measured in flight to ~ 20 db to ensure window function reconstruction

57 QUIET calibration schedule QUIET collaboration, ApJ, 2011 Overall calibration accuracy ~ 6%

58 LSPE-STRIP preliminary calibration assessment Crab visited during dedicated low-elevation scans Accuracy determined by S/N ratio Need to optimize scanning strategy to uniform calibration accuracy Montresor, 2013

59 Effect of polarization angle Polarization angle can be measured on Crab and Moon 1 accuracy can be achievable, but better is required to go below r = error on polarization angle 0.5 error on polarization angle Krachmalnicoff, 2013

60 Challenge # 4 Meeting the calibration accuracy Very tough challenge. Photometric calibration accuracy < 1% optimize scanning strategy, artificial calibrators Polarization angle better than 0.5 optimize scanning strategy, observe various sources, artificial calibrators Beam reconstruction down to 20 db can be critical for complex beams

61 Challenge # 5 Meeting the foregrounds control EBEX, Reichborn et al 2011 On selected sky patches it is possible to find relatively foreground clean regions Here we have that synctrotron is sub-dominant, but dust remains important

62 Challenge # 5 Meeting the foregrounds control WMAP, Page et al 2007 On large angular scales foregrounds dominate Foregrounds are the key issue for accurate CMB polarization measurements at large angular scales Sensitive measurements for synchrotron polarized emission control are crucial

63 Simple exercise LSPE-STRIP Error on B-mode power spectrum reconstruction Error from foregrounds with no comp. sep. Error from foregrounds with comp. sep. Error from noise with no comp. sep. Error from noise with comp. sep. Total error with no comp. sep. Total error with comp. sep. S. Ricciardi, 2012

64 Challenge # 5 Meeting the foregrounds control Extremely tough challenge. At large angular scales the polarized CMB is foreground-dominated Wide frequency measurements with high sensitivity are necessary to control synchrotron and dust Combination of data from different instruments can be an important mitigation factor

65 Conclusions Precision polarization measurements are extremely hard Several advances in detector technology available thanks to latest ground and balloon efforts Systematic effects and foregrounds are key for large scales measurements It is possible that a tensor B-mode detection will come in the next years, but certainly it is not at hand Space could be again key

66 The future from space Planck 2014 polarization results

67 The future from space LITEBIRD, Japanese (under assessment) Launch planned 2020 European (under assessment) Launch planned 2034